Signaling system



Feb, 25, 1941. H. M. PRUDEN SIGNALING SYSTEM Filed Nov. 14, 1939 HHHHHI /N l/E N TOR H. M PRI/0m WiMax/W7 A TTORNEV Patented Feb. 25, 1941 UNITED STATES PATENT OFFICE SIGNALING SYSTEM Application November 14, 1039, Serial No. 304,307

5 Claims.

This invention relates to signaling systems and particularly to systems comprising signal receiving means responsive to voice frequency signals.

Among the objects of the invention .are an increase in the reliability of Voice frequency signaling systems and the preventing of false operations of voice frequency signal receivers due to voice currents or to voice frequency currents o-ther than those to which response is desired.

The invention is a voice frequency signal receiver responsive to signals consisting of currents of two frequencies and having a particular beat frequency and responsive to signals consisting of impulses of a third frequency superimposed on the currents of the two frequencies, the receiver being non-responsive to voice currents or to voice frequency currents other than those to which response is desired.

The invention and its features will be more readily understood by considering! a signal receiver in which the invention is embodied, one such receiver being shown in the drawing which forms a part of this specification. The invention is, however, not limited in its application to the particular signaling system represented in the drawing but is generally applicable to any voice frequency signaling system.

Referring to the drawing:

Fig. 1 discloses a signal receiver comprising transformers I0, IB, 25, 20, 30 and 50, band-pass iilters Fl, F2, F3 and F4, thermionic tubes VI, V2, V3 and V4, signal receiving relays 44 and G0 and auxiliary relays 45, 65, 61 and 60; and

Fig. 2 shows the filters FI, F2, F3 and F0 in detail.

The line L to which the signal receiver is connected may be of any type, for instance, a twoconductor circuit or a phantom circuit, and is used for both signaling and talking. The line is, of course, also connected to signal transmitting means which is not shown and direction selective means are provided for preventing interference between the signal sending means and the signal receiver. Reference may be had to the patent to Crisson No. 1,755,243 of April 22, 1930 and to the patent of Meszar No. 1,835,802 of December 8, 1931 for disclosure of direction selective means suitable for use between the line L and signal receiver. The receiver is arranged so as to be nonresponsive to voice currents, to respond to voice frequency signaling currents of two particular frequencies and having a particular beat frequency, and to respond to selective impulses or signals of a third particular frequency superimposed on the two particular frequencies, Forin- (Cl. Nil-84) stance, line seizure and certain other supervisory signals received over line L may consist of current of both 1280 cycles and 1920 cycles, and selective impulses? and the disconnect signal may consist of current of 1600 cycles superimposed on the current of the other two frequencies. The signal receiver is arranged so that voice currents and voice frequency currents of frequencies other than the specified combinations of signaling frequencies do not effect a signal response, and current of all frequencies below 1200 cycles acts as a guard or blocking signal to prevent false operation. The frequencies used for signals outgoing over line L differ from the frequencies of the incoming signals. For instance, seizure and other outgoing supervisory signals may consist of current of 1440 and 2080 cycles and outgoing selective signals may consist of current of 1760 cycles. Each of the tubes Vl and V4 is a six-element vacuum tube with a suppressor grid and an indirectly heated cathode. Each of the tubes V2 and V3 is a duo-diode triode with an indirectly heated cathode. Each of the filters Fl, F2, F3 and F4 consists of inductors and capacitors of desired character. Filter Fl is designed to pass current of 1600 cycles, filter F2 to pass current of 1280 cycles, filter F3 to pass current of 1920 cycles, and iilter F4 to pass current of all frequencies below 1200 cycles. Jacks JI, J2, J3, J4 and J5 are provided to facilitate testing of the various'tube circuits. A battery for energizing the heating elements of the tubes is designated Bl and a battery for supplying the anode-cathode circuits is designated B2. Other sources of current may be used in place of these batteries. Another battery is shown, without designation, for energizing the biasing windings of relays 44 and and the windings of relays 45, B0, 0l and 68.

The line L is connected by transformer I0 to the grid of tube Vl, the voltages impressed thereon being amplified by the tube. The resistor Il and condenser I2 constitute a low-pass lter which prevents feedback from the anode to the control grid so that noise in the source of plate current cannot reach the grid. A resistor I3 is included in the cathode-anode circuit, the drop in potential through this resistor constituting a biasing voltage applied to the grid. The resistor lli and condenser I5 constitute a low-pass iilter for isolating the screen grid from the source of plate current. The condenser I6 and retard coil ll constitute a low-pass lter which prevents noise in the plate current source from entering the output circuit which includes the primary winding of transformer I8. The secondary winding of transformer I8 is connected to filters FI, F2, F3 and F4 in multiple. Current of 1600 cycles passes through filter FI and the primary Winding of transformer 50, the secondary winding being effective to impress corresponding voltages across the grid and cathode of tubev V2 as hereinafter described. Current of 1280 cycles passes through filter F2 and current of 1920 cycles passes through filter F3, the output terminals 22 and 23 of these filters being connected to the primary winding of transformer 25, thus energizing this Winding with current of the two frequencies. The resistor 26 constitutes a terminating resistance for the filters F2 and F3. Current of less than 1200 cycles passes through filter F4 and the primary winding of transformer 30, the resistor 3| constituting a terminating resistance for the filter F4 which may be used to control the sensitivity of the guard channel. Currents of all other frequencies are suppressed by the filters. The reference characters used for the terminals of the filters in Fig. 2 are the same as in Fig. 1.

The secondary winding of transformer 25 is connected in series with the lower diode of tube V2, retard coil ZB and the primary winding 0f transformer 29. The diode acts as a rectifier so that the energization of the primary winding of transformer 25 by current of the two frequencies, 1280 and 1920 cycles, effects a fluctuating `1nidirectional energization of the primary Winde ing of transformer 29. Voltages of 640 cycles, thereby induced in the secondary winding of transformer 29, are impressed across the cathode and grid of tube V4. The condenser 2`| and retard coil 28 constitute a low-pass lter which suppresses currents of 1280 and 1920 cycles passed through transformer 25 and insures the impression of current of the beat frequency and no other on the grid of tube V4. The grid biasing circuit of tube V4 is traced from the cathode through resistors 34 and 33 and the secondary winding of transformer 29 to the grid. When signaling currents of 1280 and 1920 cycles are being received over line L and there is an inconsequential current of frequencies below 1200 cycles present in line L, the beat frequency voltages impressed on the grid of tube V4 cause corresponding changes in the current in the output of tube V4 through resistor 42 in parallel with rectiiier 43 and the upper winding of relay 44 in series. The energization of the upper winding of relay 44 overcomes the energization of its lower biasing winding and effects the operation of this relay. The condenser 38 and resistor 39 constitute a low-pass filter which separates the screen grid of tube V4 from the anode circuit. The condenser 36 and retard coil 31 constitute a low-pass filter for preventing noise in the source of plate: current from being impressed on the grid of tube V4. The retard coil 40 and condenser 4| are tuned to the beat frequency so that only voltages of the beat frequency are applied to rectifier 43 to effect operation of relay 44. The resistor 42 constitutes a shunt across the rectifier and relay winding and reduces the series resistance of the tuned elements 40 and 4| to obtain satisfactory tuning characteristics.

The secondary winding of transformer 30 is connected in series with the other diode of tube V2 and the resistor 33, the diode acting as a half wave rectifier. The unidirectional current, through resistor 33, responsive to an incoming current of frequencies below 1200 cycles, causes a drop in potential in resistor 33 which increases the negative bias on the grid of tube V4. Stronger voice currents effect greater reductions in the amplification of currents of the two signaling frequencies. Thus this arrangement makes it necessary that the ratio between current of the signaling frequencies and interfering currents such as noise or voice be not less than a certain minimum value before operation of relay 44 is effected. A condenser 32 is connected across resistor 33 to maintain the drop across resistor 33 for a short interval after the occurrence of Voice currents. The resistor 34 is included in the anode-cathode circuit to provide a normal grid bias for tube V4. A condenser lay-passes resistor 34 to prevent noise in the source of plate current from reaching the grid of tube V4.

If a strong enough current of the two signaling frequencies 1280 and 1920 cycles to effect the operation of relay 44 is received over line L, relay 44 closes a circuit for operating the cut/off relay 45 and connects ground to conductor 4G to reduce the current in upper biasing winding of relay 50. The lower winding of relay 60 is normally energized in the opposite direction to the biasing Winding but due to the large normal biasing current, the armature of relay 60 is held in the position shown in the drawing. When the biasing current is reduced by the operation of relay 44, relay 60 is operated by the current normally existing in its lower Winding as hereinafter clescribed. The operation of relay 60 closes a circuit for operating relay G5. Resistors 6|, 62, 63. 64 and 65 have the resistances necessary to produce the desired control of the biasing winding of relay 60. Relay 68 closes a circuit for operating the slow-to-release relay 6l and relay 6l closes a circuit for operating relay E8. With relay 58 operated, the reduced biasing current through the upper winding of relay 50 is maintained until the two-frequency signal ends and relay 44 releases. When relay 44 releases, the current in the upper winding of relay 60 is reversed to maintain the operation of relay 69 until dial impulses are received or until a disconnect signal is received irrespective of whether the lower winding is or is not energized.

The tubes V2 and V3 constitute a detector system for controlling the signal relay E0, the lower winding of relay 60 being connected to the anodes of both of these tubes. The grid of tube V3 is normally biased to prevent current in the anode circuit. The grid biasing circuit is traced from the cathode through resistors 56 and 54 to the grid. Resistors 55 and 55 form a potentiometer circuit acrossA battery BI and the grid bias is equal to the drop in potential through resistor 56. While` there is no current of 1600 cycles in line L, the grid of tube V2 is at substantially the same potential as the cathode; and there is, therefore, a normally existing current in the anode-cathode circuit of tube V2 through the lower winding of relay 5D. Since the upper biasing Winding of relay 60 is normally energized by current in the opposite direction, relay 60 is operatively non-responsive to the energization of its lower Winding until relays 44 and 45 have operated, as above described, in response to a two-frequency signal. When a 1600 cycle current occurs in line L, the voltages induced in the secondary winding of transformer 50 cause a unidirectional current through the rectifying elements of tube V3 and resistor 5|. The condenser 52 begins to charge and the grid of tube V2 becomes more negative due to the drop in potential through resistor 5|. The condenser 53 also begins to charge in series with resistor 54. The time characteristics ef the resistor 5| and condenser 52 are short so, that-the direct current potential thereacross is at all .times substantially the same as the envelope of the voltage induced in the second-ary winding of transformer 50. The time characteristics of the condenser 53 and resistor 54 are somewhat longer than those of condenser 52 and resistor 5| butl are short enough to permit the potential of the grid of tube V3 to closely follow the envelope of the voltages induced in the secondary winding of transformer 5G. The change in the potential of the l.grid of tube V2 stops the vcurrent; through the anode and relay 6D releases. The grid of tube V3 also :becomes more negative with respect to its cathode but this is without effect since the tube is normally biased to substantially prevent current in its anode-cathode circuit. While a 1600 cycle signal isbeing received, the condensers 52 and 53 become fully charged at which time there is no further drop in potential through resistor 54 due to charging current and therefore the potential of the grid of tube V3 returns to its normal biasing value. At the end of the 1600 cycle signal, the direct current potential across resistor 5I is reduced at a rate depending on the characteristics of the lter Fl. As soon as this reduction in potential starts, the potentials of the .grids of tubes V2 and V3 become less negative due Ito the discharge of condensers 52 and. 53 and since the grid of tube V3 was just at the cut-off point, a current is immediately started through the anode of tube V3 and the winding of relay 50. Relay 80 reoperates and by the time the charge on condenser 53 is dissipated and the grid of each of tubes V2 and V3 has been restored to the normal potential, current through the anode of tube V2 maintains the operative energization of the lower Winding of relay 50. The time characteristics of the condenser 53 and resistor 54 are such that anode current in tube V3 is maintained until the anode current in tube V2 is lbuilt up suinciently to hold relay 50. Before the next 1600 cycle signal is received, the voltages in the circuit reach a steady state so that relay 60 is held by current through the anode of tube V2 and there is little or no current through the anode of tube V3. The resistor 51 prevents an excessive current through the anode of tube V2. This detector system is arranged for satisfactory transmission of dial impulses over a reasonable range of signaling energy levels even when the discharge time of the filter F4 is comparatively long.

'Ihe signaling receiver is arranged for initial response to a seizure signal comprising current of 1280 and 1020 cycles, this signal being effective to operate relay til as above described. When the signal ends and relay 44 releases, relay 60 is held by the reversal of the current in its biasing winding; so that, if 1600 cycle current is received but current of both 1280 and 1920 cycles is not being received at the same time, the deenergization of the lower winding of relay 69 in response to the 1600 cycle current will be ineiectve to cause the release of relay 5u. The` two-frequency signal is again transmitted just before dialing starts and the 1600 cycle dial impulses are superimposed on the 1280 cycle and 1920 cycle currents. Therefore, relay 44 is operated just before the first dial impulse is received to restore the current through the biasing winding to its biasing direction and thus enable the response of relay [i5 to dial impulses. When. the last impulse of a series is ended, relay 65 reoperates and when the two-frequency signal also ends, .relay Mreleases and the current .through the upper winding of relay 60 is Aagain reversed to hold rela-y 60. Supervisory signals consisting of the two frequencies eifect the operation of relays 44 and 45. A disconnect signal consists of all three frequencies, 1280 cycles, 1600 cycles and 1920 cycles, the 1600 cycle current being continuedv for a long enough interval to effect the release of relays 66, 61 and 68. If the current of the two frequencies does not continue after relay 68 releases, all relays remain normal.

Relay 4.5.is operated in response to all signals and. may control a cut-off operation on calls in which theline L is further extended to an outgoing line. In such `a case it is not desirable that dial impulses or other signals incoming over line L pass through to the outgoing line and the peration of relay d may be utilized to open the connection between the line L and the outgoing line.

In place of using rectifier elements in tubes V2 and V3 for rectifying the various signaling currents, separate rectiers may be provided and may, of course, be either half-wave or full-Wave rectiers. Other changesand modcations may be made in the signal receiver within the scope of the invention.

The signal receiver described in this specification is also disclosed in an application of R. E. Ressler Serial No. 304,305 filed on. even date herewith; but the invention Aclaimed in that application is a different invention from that claimed herein.

What'is claimed is:

1. In a signaling system, a line and a signal receiver connected to said line, said receiver comprising two signal relays, means selectively responsive to signaling current in said line of two particular frequencies for operating one of said signal relays, said means being operatively non,- responsive to current of only one of said tvvoy particular frequencies, means selectively responsive to current of a third particular frequency for operating the other signal relay, and means responsive to currents of frequencies other than said particular frequencies in case the current in said line includes said particular frequencies and other frequencies for preventing the operation of said one signal relay.

2. In a signaling system, a line and signal receiving means connected to said line, said signal receiving means comprising a signal relay and an impulse relay, circuit means responsive only to current of two particular frequencies incoming over said line for operating said signal relay, circuit means for operating said impulse relay in response to the operation of said signal relay, circuit means responsive to an impulse of current of a third particular frequency for causing the actuation of said impulse relay, and circuit means responsive to current of a frequency other than said three particular frequencies for preventing the operation of said signal relay.

3. In a signaling system, a line, two relays, one for response to signals consisting of current of two parti-cular frequencies in said line, the other for response to signals consisting of current of a third particular frequency superimposed on current of said two frequencies, a detector, the output of said detector connected to said one of the relays, means comprising a lter tuned to pass currents of said two frequencies and to suppress other currents connecting said line to the input of said detector, another detector, the output of said other detector connected to the other of said relays, means comprising a filter tuned to pass current of said third particular frequency and to suppress other frequencies connecting said line to the input of said other detector, and

i means responsive to currents of frequencies other than said particular frequencies in case the lcurrent in said line includes said particular frequencies and other frequencies for preventing the operation of said one of the relays.

4. In a` signaling system, a line, two relays, one for response to signals consisting of current of two particular frequencies in said line, the other for response to signals consisting of current oi a third particular frequency, a rectifier, the output of said rectifier connected to said one of the relays, an amplifier, means tuned to pass cur rents of a frequency equal to the difference between said two frequencies connecting the output of said amplifier to the input of said rectifier, an-

'other rectifier, means comprising a filter tuned to pass currents of said two particular frequencies connecting said line to the input of said other rectifier, means connecting the output of said other rectifier to the input of said amplifier, a third rectifier, the output of said third rectifier' connected to the other of said relays, means ccm prising a filter tuned to said third particular frequency connecting said line to the input of said third rectifier, and means responsive to currents of frequencies other than said particular frequencies in case the current in said line includes said particular frequencies and other frequencies for preventing the operation of said cnc ci the relays.

5. In a signaling system, a line, two relays, one for response to signals consisting of current of two particular frequencies in said line, the other for response to signals consisting of current of a third particular frequency superimposed on currents of said two frequencies, a rectifier, the output of said rectifier connected to said one of the relays, an amplifier, means tuned to pass currents of a frequency equal to thel difference he tween said tWo frequencies connecting the output of said amplifier to ythe input of said rectifier, another rectifier, means comprising a filter tuned to pass currents of said two particular frequencies connecting said line to the input of said other rectifier, means connecting the output of said other rectifier to the input of said amplifier, a third rectifier, the output of said third rectifier connected to the other of said relays, means comprising a filter tuned to said third particular Irequency connecting said line to the input of said third rectifier, means comprising said one relay enabling the response of said other relay to current of said third frequency superimposed on current of said two frequencies, and means responsive to currents of frequencies other than said particular frequencies in case the current in said line includes said particular frequencies and oth er frequencies for preventing the operation of said one of the relays.

HAROLD M. PRUDEN. 

